Method of producing biodiesel fuel

ABSTRACT

A method of producing biodiesel fuel from fats and oils includes a step of transesterification reaction in which fats and oils are transesterfied with lower alcohol, a step of fuel refining in which a resultant fatty acid alkyl ester produced in said transesterfication reaction step is refined, and a mixing step in which the fatty acid alkyl ester refined in the fuel refining step is mixed with light oil. The refined fatty acid alkyl ester is heated to a predetermined temperature and thus fused so as not to oxidize unsaturated fatty acids contained in the fatty acid alkyl ester, while the heated and refined fatty acid alkyl ester is mixed with light oil so as not to set the temperature of the mixed solution below the cold filter plugging point during the mixture, to dilute the fatty acid alkyl ester by light oil to a predetermined weight ratio.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of producing biodiesel fuel, in particular, relates to the method of producing biodiesel fuel which is capable of reliably being used as a fuel without causing any clog of an engine filter, etc., in a case where the biodiesel fuel is used for a fuel of an internal engine.

2. Discussion of the Related Art

Recently, much attention has been paid to so-called bio-fuel, biodiesel fuel, in particular for the following reasons, so that its R&D has been carried out.

Firstly, the biodiesel fuel is generally produced by reacting fats and oils from plants or from animals with methanol to produce methyl ester, and then, mixing the resultant fatty acid methyl ester with light oil with a predetermined ratio (refer to Japanese Patent Laid-open Publications HEI07-197047, HEI10-245586, and 2002-167356). For this reason, since the biodiesel fuel contains substantially no sulfur gradients, the amount of the toxic exhaustion gas such as black smoke is small, so that it is environmentally friendly fuel.

Secondly, since the biodiesel fuel is derived from plants, the discharge amount of carbon dioxide is counted to be zero under the specification issued in “KYOTO PROTOCOL”.

As stated above, much attention has been paid to the biodiesel fuel as an environmentally friendly fuel alternative to light oil, however, in Japan, as compared to European countries, it has been used only by municipal organizations, etc. In addition, in Japan, at present, the weight ratio of fatty acid methyl ester to light oil is specified to be 5% at most.

Since such fatty acid methyl ester produced in the above processes comprises saturated fatty acids and unsaturated fatty acids, the following technical problems have arisen.

That is to say, in a case where the fatty acid methyl ester is mixed with light oil by the predetermined ratio, deposits (insoluble) can be generated, so that an engine filter can be clogged in a case where the biodiesel fuel is fed to the internal engine, and as a result, a scenario in which the biodiesel cannot be used as a fuel can be brought about.

More specifically, in a case where palm oil is used as fats and oils from plants, fatty acid constituting palm oil comprises myristic acid (saturated fatty acid, melting point of 54° C.) with 1.1%, palmitic acid(saturated fatty acid, melting point of 63° C.) with 44.4%, stearic acid (saturated fatty acid, melting point of 69° C.) with 4.3%, oleic acid (unsaturated fatty acid, melting point of 13.4° C.) with 39.9%, linoleic acid (unsaturated fatty acid, melting point of 5° C.) with 9.4%, so that respective methyl ester produced from the respective fatty acids are myristic acid methyl ester (melting point of 19.5° C.), palmitic acid methyl ester (melting point of 31° C.), stearic acid methyl ester (melting point of 37.8° C.), oleic acid methyl ester (melting point of 10.5° C.), and linoleic acid methyl ester(melting point of 9.5° C.).

In such a case, generally speaking, the melting point of unsaturated fatty acid is lower than that of saturated fatty acid, so that the higher the ratio of unsaturated fatty acid to saturated fatty acid becomes, the melting point of the fatty acid methyl ester becomes lower. For instance, in a case where the biodiesel fuel is used in a winter season, it can be used as a liquid fuel.

However, firstly, as compared to saturated fatty acid, unsaturated fatty acid tends to be readily oxidized. That is why unsaturated fatty acids contained in the fatty methyl ester is caused to be oxidized by the fact that it is subject to air in a case where the fatty acid methyl ester is mixed with light oil by the predetermined ratio, so that hydroperoxicide which is an oxidization product can separate out as insoluble, thereby causing the above engine filter to be clogged.

Secondly, in a case where the fatty acid methyl ester is mixed with light oil by a predetermined ratio, the deposit can be caused by the fact that the temperature of the mixed fuel is inadvertently lowered to below the cold filter plugging point due to a negligence of the temperature control.

More specifically, even if the fatty acid methyl ester constitutes saturated fatty acid, if the fatty acid methyl ester with a high concentration is set to be below the cold filter plugging point, the insoluble with a high melting point can be generated.

In a cold climate area, light oil for a diesel engine can cause a clogging phenomenon of a fuel system. In order to evaluate such a phenomenon, the cold filter plugging point is defined to be a temperature in which a clogging is caused by a deposited wax by the fuel oil being filtered under a predetermined depressurized condition while cooled.

Since said first technical problem becomes serious as the temperature of the fatty acid methyl ester becomes higher, while said second technical problem becomes serious as the temperature of the fatty acid methyl ester becomes lower like a winter season, it is strongly desired that both first and second technical problems are solved simultaneously.

SUMMARY OF THE INVENTION

An object of an embodiment of the present invention is to provide a method of producing biodiesel fuel which is capable of reliably being used for a biodiesel fuel without causing insoluble in the mixed solution, in a case where the biodiesel fuel is produced by mixing fatty acid methyl ester with light oil.

According to an embodiment of the present invention, there is provided a method of producing biodiesel fuel from fats and oils comprising (i) transesterifying fats and oils with lower alcohol to produce a fatty acid alkyl ester; (ii) refining the fatty acid alkyl ester; (iii) heating the refined fatty acid alky ester to fuse the refined fatty acid alky ester; and (iv) mixing the fused fatty acid alkyl ester with light oil to produce a mixed solution, wherein step (iii) comprises heating the refined fatty acid alkyl ester to a temperature such that a temperature of the mixed solution during step (iv) becomes equal to or higher than its cold filter plugging point (CFPP) but lower than a temperature at which unsaturated fatty acids contained in the fused fatty acid alkyl ester are substantially oxidized.

According to an embodiment of the present invention, the method of producing biodiesel fuel which is capable of reliably being used for a biodiesel fuel without causing insoluble in the mixed solution is characterizable by oxidizing unsaturated fatty acids contained in the fatty acid alkyl ester as little as possible, while at the same time by mixing the fatty acid alkyl ester with light oil in a temperature controlling manner so as not to set the mixed solution below the cold filter plugging point.

Since in a winter season, in particular, the fatty acid alkyl ester refined in the fuel refining process is naturally caused to be solidified in a container, the oxidization of the fatty acid alkyl ester can be prevented from being accelerated by storing said solid fatty acid alkyl ester in the container in a sealed manner, while at the same time, the acceleration of the oxidization of the fatty acid alkyl ester can be restricted by the fact that the fatty acid alkyl ester is heated from the outside of the container immediately before the mixing process so as to fuse the fatty acid alkyl ester. Further, the deposit of the insoluble can be effectively prevented by mixing the fatty acid alkyl ester with light oil so as not to set the temperature of the mixed solution below the cold filter plugging point during the mixing process in a cold ambient temperature.

According to a preferred configuration, the step (iv) is subdivided into multiple steps and performed at substantially or nearly an ambient temperature step-by-step.

According to a preferred configuration, the step (iii) is performed under a substantially sealed condition to substantially block air and/or light.

According to a preferred configuration, the lower alcohol is methyl alcohol.

According to a preferred configuration, the fats and oils is one material selected from plants and animals.

According to a preferred configuration, the fats and oils is palm oil.

According to a preferred configuration, the method further comprising removing solids and/or water from the fats and oils by gravity separation.

According to a preferred configuration, the step (i) is performed using a non-oxidizing catalyst.

According to a preferred configuration, the non-oxidizing catalyst is potassium hydroxide.

According to a preferred configuration, the step (ii) further comprises filling a container with the refined fatty acid alkyl ester and storing the refined fatty acid alkyl ester in solid form within the container under a sealed condition, and step (iii) comprises heating the solid fatty acid alkyl ester from outside the container while the container is sealed, thereby fusing the the solid fatty acid alkyl ester.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a view showing a general process in which the biodiesel fuel is produced by the method according to an embodiment of the present invention.

FIG. 2 is a view showing a minute process in the transesterification reaction process in FIG. 1.

FIG. 3 is a view showing a minute process in the mixing process in which the fatty acid alkyl ester is mixed with light oil.

FIG. 4 is a view showing a general structure of a mixing and stirring apparatus used in the second mixing process in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

The method of producing biodiesel fuel according to an embodiment of the present invention now will be described with reference to the drawings. In this embodiment, palm oil and methyl alcohol are adopted as fats and oils, and lower alcohol, respectively, as examples.

As shown in FIG. 1, the method of producing biodiesel fuel according to an embodiment of the present invention, generally comprises a transesterification reaction step 16 of transesterifying fats and oils 12 with lower alcohol 14, a fuel refining step 18 of refining fatty acid alkyl ester produced in the transesterification reaction step 16, and a mixing step 22 of mixing fatty acid alkyl ester refined in the fuel refining step with light oil 20.

The fats and oils 12 may be stored in a tank by which solid impurities contained in the fats and oils can be filtered by means of a filter, for instance. The fats and oils may be the ones from plants or animals,(or waste oil which has resulted from these oils being used for cooking), and with respect to the plant fats and oils, palm oil, corn oil, soy oil, rape oil, coconut oil, etc. may be adopted, while with respect to the animal fats and oils, oil from cow, lard, and fish oil, etc. may be adopted.

The transesterification reaction step 16 may be a conventional known step, as shown in FIG. 2. The transesterification reaction step 16 generally comprises a step 24 of regulating a catalyst solution, a step 28 of transesterifying fats and oils with alcohol solution containing the catalyst 26, and a step 32 of removing excessive alcohol 30 under a depressurized condition from the reacted mixed solution produced in the former step.

In the transesterification process 16, fats and oils 12 are heated and depressurized in advance by a heat exchanger, a hydrator and a deodorizing reactor (not shown) so as to contain a predetermined water content (less than 0.05%, for instance) and a predetermined odor content (less than 0.01%, for instance).

In the regulating process 24 of the catalyst solution, a stirring container (not shown) is used, for instance, and metered alcohol is fed into the container, and then, the alcohol in the container is stirred, while at the same time, the catalyst 26 with a predetermined ratio is fed into the container in a batch manner in order for catalyst to be dissolved into the alcohol.

The catalyst 26 used in the regulating process may be alkali base, sodium hydroxide, potassium hydroxide, etc., the alcohol 14 may be lower alcohol such as methyl alcohol, propyl alcohol, etc.

In the transesterification process 28, a reaction mixing tank (not shown) may be used where alcohol solution containing the catalyst is continuously mixed with the fats and oils 12 pretreated as described above.

In the removing process 32 under the depressurized condition, excessive alcohol 30 is removed under the depressurized condition from the reacted mixed solution produced in the transesterification reacting process 28, whereby, in the next fuel refining process 18, the reacted mixed solution in which the excessive alcohol 30 is removed under the depressurized condition is treated by an absorber or a filter, etc., for instance.

In the fuel refining process 18, alkyl ester which is the object product is obtained by separating alkyl ester from glycerine by means of a centrifugal separating process, for instance.

By the above conventional processes, the desired degree of conversion of the ester and the desired acid number can be accomplished.

As shown in FIG. 3, the mixing process 22 in which fatty acid alkyl ester is mixed with light oil generally comprises a heating process 34 in which fatty acid alkyl ester is heated and thus fused, a first mixing process 36 in which fused fatty acid alkyl ester is mixed with a small amount of light oil 20, and a second mixing process 38 in which mixed solution produced in the first mixing process 36 is mixed with a large amount of light oil 20.

In the heating process 34 of fatty acid alkyl ester, a steel drum is filled with a predetermined amount of fatty acid alkyl ester produced in the transesterification reaction process 16, and then, uniformly heated and the temperature of fatty acid alkyl ester is maintained to be constant by winding a band type heater on the outer periphery of the steel drum, while at the same time controlling the temperature of fatty acid alkyl ester by means of a thermostat, etc. This causes the fatty acid alkyl ester in a setup condition within the steel drum to be prevented from being oxidized in an accelerated manner by the fact that the steel drum is stored in a sealed situation, while at the same time to restrict the oxidization thereof by heating the steel drum from its outside, in a case where the fatty acid alkyl ester is fused. At this stage, the temperature at which the fatty acid alkyl ester is heated may be preferably high, from the technical point of view that the mixed solution is set not to be below the cold filter plugging point in a case where it is mixed with light oil, while on the other hand, if such a temperature is so high, unsaturated fatty acid becomes oxidized to generate deposits. Accordingly, the temperature at which the fatty acid alkyl ester is heated may be preferably determined so as to meet the above both matters. In addition, in a case where the fatty acid alkyl ester is heated to a certain temperature, it may be preferably fused under a substantially sealed condition so as to be subjected to light and oxygen in the air as little as possible.

In the first mixing process 36, the fatty acid alkyl ester is mixed with light oil stored under an ambient temperature so as to set the weight ratio of the fatty acid alkyl ester to light oil to be 50%.

FIG. 4 is a general view showing a mixing and stirring apparatus 40 used in the second mixing process 38. The mixing and stirring apparatus 40 comprises a tank 42 with a large volume which is filled with light oil, a stirring machine 44 disposed to be the upper portion of the tank 42, a circulating tube 50 connecting between a lower outlet opening 46 of the tank 42 and the upper inlet opening 48 thereof, a strainer 52 disposed to be in the intermediate portion of the circulating tube 50 and adjacent to the lower outlet opening 46, and a pump 54 disposed to be downstream of the strainer 52.

The stirring machine 44 includes stirring blades 56 rotatable about a vertical axial line of the tank 42 at a lower portion and an intermediate portion of the tank 42, respectively. The solution in the tank 42 can be uniformly stirred and thus mixed by rotating the stirring blades 56.

According to the above structure, the tank 42 is filled with the mixed solution with 50% concentration produced in the first mixing process, and then, it is further mixed with light oil within the tank 42, whereby such mixed solution is adapted to be stirred and thus mixed in the tank 42 by circulating it through the circulating tube 50 by means of the pump 54.

The inventor confirmed the effect of the method of producing biodiesel fuel according to an embodiment of the present invention by carrying out comparison experiments in which the temperatures of fatty acid alkyl ester and light oil gas were different, adopting the above producing method.

The main experimental conditions were as follows.

-   -   (1) Fats and oils: palm oil     -   (2) Lower alcohol: methyl alcohol     -   (3) Method of producing fatty acid alkyl ester: alkaline         catalyst method     -   (4) Final mixing ratio of fatty acid alkyl ester to light oil:         4.75%

The main experimental processes were as follows.

Firstly, fatty acid alkyl ester produced by the transesterification reaction of methyl alcohol under alkaline catalyst was prepared in advance, and the tank 12 was filled with light oil (14000 litter). In this connection, the fatty acid alkyl ester was stored in a setup condition within the sealed tank, and in a case where it was used in the mixing process, it was fused by heating from the outside immediately before the mixing process.

In the first mixing process, an empty metal drum was filled with fatty acid alkyl ester (100 litter) whose heating temperature was maintained to be a predetermined temperature and light oil with an ambient temperature (100 litter) from the large tank. Then, they were stirred and mixed to make the weight ratio of the fatty acid alkyl ester 50%. Three cans of said metal drums were prepared.

Then, in the second mixing process, the large tank of the second mixing apparatus was filled with the mixed solution in the metal drum prepared in the first mixing process, and then stirred by the stirring machine, circulated through the circulating tube by means of the pump until the mixed solution became a stable condition.

It was then confirmed whether or not the deposit was captured by the strainer.

(Experiment 1)

The temperatures of fatty acid alkyl ester and light oil were measured to be 50° C. and 8° C., respectively, and it was confirmed that the deposit rapidly separated out as wax ingredient.

This phenomenon is verified by the following calculation related to the relationship of the thermal capacity between fatty acid alkyl ester, light oil and the mixed solution.

The temperature of the mixed solution produced in the first mixing process is calculated to be 29° C. by the following equation.

100(litter)×50(° C.)+100(litter)×8(° C.)=200(litter)×29(° C.)

Then, the temperature of the mixed solution within the large tank produced in the second mixing process is calculated as follows, since the light oil remaining in the large tank is 13, 700 (litter)(14,000−300).

600(litter)×29(° C.)+13,700(litter)×8(° C.)=8.88(° C.)×14,300(litter)

As stated above, the temperature of the mixed solution within the large tank was confirmed to be 8.88° C. which is below the cold filter plugging point of the fatty acid alkyl ester, that is why the deposit rapidly separated out as wax ingredient.

(Experiment 2)

The temperatures of fatty acid alkyl ester and light oil were measured to be 54° C. and 9.5° C., respectively, and it was confirmed that the deposit did not separate out as wax ingredient.

This phenomenon is verified by the following calculation related to the relationship of the thermal capacity between fatty acid alkyl ester, light oil and the mixed solution.

The temperature of the mixed solution produced in the first mixing process is calculated to be 31.75° C. by the following equation.

100(litter)×54(° C.)+100(litter)×9.5(° C.)=200(litter)×31.75(° C.)

Then, the temperature of the mixed solution within the large tank produced in the second mixing process is calculated as follows, since the light oil remaining in the large tank is 13, 700 (litter)(14,000−300).

600(litter)×31.75(° C.)+13,700(litter)×9.5(° C.)=10.4(° C.)×14,300(litter)

As stated above, the temperature of the mixed solution within the large tank was confirmed to be 10.4° C. which is higher than the cold filter plugging point of the fatty acid alkyl ester. Accordingly, it was verified the reason why the deposit did not separate out. In addition, even if the temperature of the mixed solution becomes below the cold filter plugging point after the fatty acid alkyl ester is finally mixed with light oil up to 4.75%, it was confirmed that the deposit did not separate out due to the freezing point depression.

(Experiment 3)

The temperatures of fatty acid alkyl ester and light oil were measured to be 54° C. and 9.0° C., respectively, and it was confirmed that the deposit separated out as wax ingredient, but that, as compared to the experiment 1, the amount of the deposition was less than that in the experiment 1.

This phenomenon is verified by the following calculation related to the relationship of the thermal capacity between fatty acid alkyl ester, light oil and the mixed solution.

The temperature of the mixed solution produced in the first mixing process is calculated to be 31.5° C. by the following equation.

100(litter)×54(° C.)+100(litter)×9.0(° C.)=200(litter)×31.5(° C.)

Then, the temperature of the mixed solution within the large tank produced in the second mixing process is calculated as follows, since the volume of the light oil remaining in the large tank is 13, 700 (litter)(14,000−300).

600(litter)×31.5(° C.)+13,700(litter)×9.0(° C.)=9.94(° C.)×14,300(litter)

As stated above, the temperature of the mixed solution within the large tank was confirmed to be 9.94° C. which is below the cold filter plugging point of the fatty acid alkyl ester. It was considered that is why the deposit separated out as wax gradient, and why the amount of the deposit in this experiment was less than that in the first experiment.

As stated above, the inventor confirmed that in a case where fatty acid alkyl ester is heated while it is not oxidized, and then, fatty acid alkyl ester is mixed with light oil, it is important that the temperature of the mixing solution containing the fatty acid alkyl ester with a high concentration is maintained to be higher than the cold filter plugging point.

According to the method of producing biodiesel of an embodiment of the present invention, since the method of producing such a fuel which is capable of reliably used as a biodiesel fuel without causing any insoluble can be provided, and in a case where it is used for an internal engine as an alternative to light oil, it can be reliably used as a fuel without causing any clogging in an engine filter, etc., the embodiment of the present invention is industrially applicable.

As described above, the preferred embodiments of the present invention were described in detail, however, those skilled in the art can modify, or change in various manners without departing from the scope of the present invention. For instance, in this embodiment, palm oil is adopted as the fats and oils, while methyl alcohol is adopted as the lower alcohol, however, the fats and oils from animals, or waste fats and oils may be adopted. In addition, in this embodiment, fatty acid alkyl ester was mixed in two stages with light oil so as to set a weight ratio thereof to be 5% (4.75%), however, more multiple mixing manner may be appropriately adopted, in accordance with an amount of biodiesel to be produced and an ambient temperature at which light oil is stored. Further, in this embodiment, the produced fatty acid alkyl ester was once solidified in the container and stored under a sealed condition, and it was fused by heating it from outside immediately before the mixing process, however, so long as unsaturated fatty acids contained in the fatty acid alkyl ester is not oxidized, the fuel refining process of the fatty acid alkyl ester and the mixing process of the fatty acid alkyl ester with light oil do not have to be carried out in a batch manner, but may be carried out in an on-line manner.

In the present disclosure where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation.

The present application claims priority to Japanese Patent Application No. 2008-192912, filed Jul. 26, 2008, the disclosure of which is incorporated herein by reference in its entirety. 

1. A method of producing biodiesel fuel from fats and oils comprising: (i) transesterifying fats and oils with lower alcohol to produce a fatty acid alkyl ester; (ii) refining the fatty acid alkyl ester; (iii) heating the refined fatty acid alky ester to fuse the refined fatty acid alky ester; and (iv) mixing the fused fatty acid alkyl ester with light oil to produce a mixed solution, wherein step (iii) comprises heating the refined fatty acid alkyl ester to a temperature such that a temperature of the mixed solution during step (iv) becomes equal to or higher than its cold filter plugging point (CFPP) but lower than a temperature at which unsaturated fatty acids contained in the fused fatty acid alkyl ester are substantially oxidized.
 2. The method according to claim 1, wherein step (iv) is subdivided into multiple steps and performed at substantially or nearly an ambient temperature step-by-step.
 3. The method according to claim 1, wherein step (iii) is performed under a substantially sealed condition to substantially block air and/or light.
 4. The method according to claim 1, wherein the lower alcohol is methyl alcohol.
 5. The method according to claim 1, wherein the fats and oils is one material selected from plants and animals.
 6. The method according to claim 5, wherein the fats and oils is palm oil.
 7. The method according to claim 1, further comprising removing solids and/or water from the fats and oils by gravity separation.
 8. The method according to claim 1, wherein step (i) is performed using a non-oxidizing catalyst.
 9. The method according to claim 8, wherein the non-oxidizing catalyst is potassium hydroxide.
 10. The method according to claim 1, wherein step (ii) further comprises filling a container with the refined fatty acid alkyl ester and storing the refined fatty acid alkyl ester in solid form within the container under a sealed condition, and step (iii) comprises heating the solid fatty acid alkyl ester from outside the container while the container is sealed, thereby fusing the the solid fatty acid alkyl ester. 